In part 2 celiac disease patients, non-celiac gluten sensitive subjects and healthy controls will be recruited and they will be divided into four groups: oat-avoiding celiacs (1), oat-consuming celiacs (2), non-celiac gluten sensitive subjects (3) and healthy controls (4). Recruiting aim for each group is 15 subjects. In addition to dietary data, a blood, and a fecal sample will be collected from the subjects. The gut microbiota will be analyzed from the fecal samples. The metabolic products will be analyzed from the fecal, urine and blood samples. The gut microbiota composition will be analyzed with next-generation DNA sequencing techniques.